Photosensitivity has been found in polymers having an all silicon backbone such as in A) linear poly(diorganosilylenes), sometimes called polysilylenes or polysilanes, i.e., materials having the general formula [R.sup.1 R.sup.2 Si].sub.n with R.sup.1 and R.sup.2 being various alkyl or aryl substituents and having n typically larger than 20, and B) in polysilyne network materials, i.e., materials having at least 70% of their silicon atoms bound to only one organic substituent and to three other silicon atoms.
Irradiation of linear polysilylenes with UV or deep UV light generally causes fragmentation that results after development in positive images--the unexposed regions remain after development. The photoreactivity of polysilynes is markedly different from that of polysilylenes. The polysilyne layer is exposed to ultraviolet light in the presence of oxygen to induce photooxidation with formation of crosslinked Si--O--Si networks. Such photooxidation produces changes in chemical behavior, solubility, and in the refractive index of the oxidized relative to the unoxidized regions. The photooxidation allows selective removal by suitable solvents or halogen-based plasma reactive ion etching of the unexposed region to produce a negative image. Thus, photooxidation processes in polysilynes are suitable for fabrication of optical and electronic devices. (See U.S. Pat. No. 4,921,321, dated May 1, 1991.)
Organosilicon films of partially characterized structure (reported in M. W. Horn et al, Journal of Vacuum Science and Technology, B8, 1493 (1990), that contain substantial Si--C--Si backbone bonds and an insignificant presence of Si--(Si)--Si bonds), have been deposited by plasma reaction of various volatile organosilicon compounds such as tetramethylsilane. These materials show a decrease in solubility and increased resistance to gaseous HBr or chlorine plasma etching after exposure to light at 193 nm with sensitivities of approximately 50 mJcm.sup.-2, but are essentially transparent and not useful at longer wavelengths such as at 248 nm. For many processes such as the formation of electronic and optical devices, photosensitive materials (denominated resists) having a photosensitivity better than 200 mJcm.sup.-2 and preferably better than 100 mJcm.sup.-2 at or above 248 nm are required to avoid undesirably long exposure times. (Photosensitivity is defined as exposure dose required to allow the development of an imaged film capable of functioning as an effective etch mask for subsequent pattern transfer by reactive ion etching.)
Silicon polymers deposited from a gas phase are described in U.S. Pat. No. 5,439,780 to Joshi et al. These polymers, formed from precursors such as methylsilane, ethylsilane, and phenylsilane, provide a substantial bonded network of Si--(Si).sub.n --Si which is sensitive to light at wavelengths in the ultraviolet (UV) and deep UV range. When these polymers are exposed to radiation at these wavelengths in the presence of oxygen, a siloxane network forms in the exposed regions selectively. In this manner, a selectivity is introduced into the exposed resist which is exploited to develop the image of the pattern in the resist.
However, Joshi et al. utilize aqueous hydrofluoric (HF) acid as a developer for positive-tone resists. Although patterns can be developed using an aqueous HF etchant, there is a possibility that particles of resist will remain on the substrate in the areas from which the resist was intended to be removed. The presence of these particles adversely affects the subsequent transfer of the developed pattern into the underlying substrate. Accordingly, methods of development less susceptible to leaving particle residues which are also compatible with the cluster tool are desired. One advantage of polymers deposited from the gas phase is that resist formation, exposure, development, and pattern transfer are possible within an interconnected series of chambers (sometimes referred to as a cluster tool ).
It has long been a goal to form a suitable resist on a substrate by deposition from the gas phase, useful for conventional deep to mid-UV photolithography (for example, at 193, 248, 310, or 365 nm). Such gas phase deposition is advantageous since resist formation, exposure, development, and pattern transfer would become possible within an interconnected series of chambers (sometimes called a cluster tool) without degradation resulting from exposing the wafer to the ambient. In this regard, a process for developing a positive tone pattern in such resists that is compatible with the cluster tool is also desired.